Asked by: Jamie Malley, By Email
They didn’t. Nothing that’s still alive has stopped evolving. Change continues, and some individuals live while others die. So evolution cannot stop. It’s true that crocodiles haven’t changed much over millions of years, but that’s because they’re so successful at exploiting a niche that hasn’t changed much either.
What is curious about modern crocodiles is that their land-based ancestors, that walked on two legs, somehow survived whatever wiped the dinosaurs out about 65 million years ago. Modern crocodiles still have hind legs longer than front legs inherited from them. When they evolved into aquatic creatures they had to avoid breathing water and so evolved a second palate in the roof of the mouth to keep air and water apart.
Crocodiles will probably keep evolving while looking and behaving much the same as long as their niche of warm food-rich waters survives. Otherwise they will have to change to adapt or go extinct as so many other creatures have before them.